Electrostatic printing tube having unique anode structure



Nov. 17, 1964 J. J. STONE, JR 7,

ELECTROSTATIC PRINTING TUBE HAVING UNIQUE ANODE STRUCTUR Filed March 14,1960 FIG. 1

DEFLECT/ON SIGNAL sou/m5 livmvslrr CONTROL SIGNAL SOURCE FIG 3 {PR/0RART) la. 2

INVENTOR. Joseph James Sfone Jr BY United States Patent O 3,157,811ELECTRQSTATIC PRINTHNG TUBE HAVENG UNHQUE ANUDE STRUCTURE loseph JamesStone, in, Gienview, ill, assignor to A. B. Dish Company, Niles, lit, acorporation of lllinois Filed Mar. 14, 195i), Ser. No. 14,686 4 Claims.(ill. 313-43) This invention relates in general to an improvedelectrostatic printing arrangement, and more particularly to anarrangement for improving both the resolution of images secured by meansof electrostatic printing tubes and the tube structure.

In known electrostatic printing arrangements such as that disclosed inan application by John S. Tregay, lr., filed May 10, 1957, Serial No.658,275, now abandoned a conventional cathode ray tube is modified bythe .provision of an array of wires in its face which extend from theinterior surface of the face to the exterior surface. A high voltagebeam of electrons is varied in accordance with a desired image andtraverses the interior terminations of the array of wires embedded inthe non-conductive face of the tube to cause a discharge through adielectric or printing paper passing adjacent to the exterior wireterminations at a desired speed. This arrangement although producingsatisfactory images does give rise to some ditiiculties in resolutiondue to the capacitive eifect of the wires in the matrix.

Thus the dielectric is located between the wires and an exteriorelectrode maintained at ground or anode potential, while the respectiveWires are charged toward the cathode potential. This creates a chargedcondition therebetween which is satisfied only by discharge through thedielectric, and on initiation of the discharge, it continues untilcomplete. If the discharge period is extended, it may result in poordefinition of the discharge area marked on the dielectric.

In addition, problems arising from high beam currents, the wire to wirecapacitance, secondary emission and a host of interrelated electricalconditions, all contribute to the problems of securing good reliableimage resolution.

It is, therefore, proposed by the present invention to electrically loadeach wire to alleviate the described bstacles.

The effect of loading or biasing on the Wires to a value just below thedischarge or writing potential makes possible a decrease in the electronbeam current required to drive the wires above the writing potential. Itfurther reduces the intercapacitive effects between the wire and enablesthe collection of secondary electrons.

To accomplish this, the conductor or wire adjacent to the inner surfaceof the tube face and a portion of the inner face are etched away to formdepressions at the wires. A conductive coating is then applied to theinner tube surface with a thinner conductive coating deposited in thedepressions, after which the coating may be either grounded or connectedto an external voltage source. The grid structure forming the overallinner surface coating, thus collects secondary electrons to permitincreased resolution by restricting the writing area. Thereducedparallel length of each wire also serves to reduce its capacitive effectand permits the use of a larger number of wires. Thus the use of thickermatrix arrays provides a more sturdy tube arrangement.

Accordingly, it is an object of the present invention to provide anelectrostatic printing tube having improved image resolution.

It is another object of the present invention to provide an improvedmeans for reducing capacitance between the printing wires of the arrayand the electrostatic printing tube.

' 3,15I,8ll Patented Nov. 17, 1954 it is another object of the presentinvention to provide an arrangement permitting the use of lower beamcurrent in an electrostatic printing tube.

Another object is to increase the sensitivity of an electrostaticprinting tube by providing an improved bias arrangement for the wirearray.

It is still another object of this invention to reduce the eifects ofsecondary electrons in an electrostatic printing tube.

A feature of this invention is the means for biasing the wires of anarray in an electrostatic printing tube.

It is another feature of this invention to coat the interior surface ofthe face of an electrostatic printing tube with a conductive materialfor reducing capacitive and secondary electron effect.

These and other objects, features and advantages of this invention willbecome apparent on reading the following specifications and claims inconjunction with the drawings of which:

FIG. 1 is a standard cathode ray tube of the type used in electrostaticprinting modified by the application of an inner surface coating.

FIG. 2 is a partial sectional view showing the manner in which a wireconductor is arranged in the usual electrostatic printing tube.

FIG. 3 is a sectional view similar to FIG. 2, showing a portion of innersurface .and wire as etched away and FIGS. 4 and 5 show respective frontand side views of portions of the tube face with the conductive coatingapplied.

Referring now to FIG. 1 showing a cross section of the electrostaticprinting tube incorporating the principles of the present invention, itwill be seen that the tube indicated at lit) is similar to aconventional cathode ray tube. It includes an evacuated envelope 12,which carries a cathode 14, a control grid 13 connected to a suitablesignal source 15, an anode or accelerating electrode 16, a focus coil 18and a deflection coil 20. The cathode is connected to the negativeterminal of high voltage supply 22.

The deflection coil 2G is controlled from a suitable defiection signalsource 28, for controlling the beam produced at the cathode 14 while thebeam is modulated by the si nals from source 15 for reproducing an imagerepresented by those signals.

In addition, the tube includes any well known type of face plate 32 ofdielectric material in which the wires 34 are carried or embedded.Adjacent the terminations of the wires, exterior of the tube, a suitabledielectric material 36 is provided for recording the image. It is movedin the direction indicated by the arrow and has associated on its otherside a conductor 38, at ground potential whereby discharge from thewires through the dielectric is accomplished.

In operation, the electron beam is of course directed to the variouswires 34, in accordance with the desired scanning rate, while the imagereproducing dielectric 36 passes adjacent the external terminations ofthe wires.

The control grid 13 is controlled in accordance with the signalsintroduced thereto from signal source 15. These signals represent theimage to be reproduced and modulate the beam emitted by 14 accordingly.

The potential source 22 furnishes a voltage of sufiicient magnitude toprovide a beam which need not be operated at the high voltagespreviously used, but instead at just above the writing voltage. This isdue to the bias voltage applied to the wires 34 through coating 62. Inaddition, by the suitable choice of bias values, secondary electronsemitted as a result of the beam striking the face or Wires are preventedfrom migrating to the exterior face to affect image resolutions.

Thus each wire 34 is energized in sequence and repetitively as the beamsweeps across the tube face at a rate determined by the deflectionsignal source 28.

The degree of charge imparted to each wire 34 is dependent on themodulation from signal source 15 at the time of impact. Due to thereduced parallel length of the wires 34, the capacitance between thewires is substan tially reduced. Because of this, and factors alreadydiscussed, the decay time of each discharge between a wire 34, throughdielectric 36 to ground at 38, is considerably shortened and otherwiseconfined to provide improved image resolution.

Referring now to FIG. 2 in which a portion of the face plate 55a of astandard electrostatic printing tube is shown, it will be seen that theprinting wire 34a extends from the interior surface 56 to the exteriorsurface 57. In accordance with the practice of this invention, theinterior surface 56 adjacent each wire 34 is etched away to form arecess 60, see FIGURE 3, in the interior surface adjacent each wire ofthe matrix and the wire indicated at 34 is shortened. The inner orinterior surface 56 of the tube is then coated with a conductivematerial such as 62 which is also deposited in a thin layer 64 in eachrecess 60, as shown in FIGS. 4 and 5. Controlling the thickness of thedeposit or coatings 62 and 64 by vapor depositation from a source in avacuum located, for example, in a plane parallel to surface 56, causesthe deposit to be of variable thickness and enables it to exercisecertain control functions such as electrical isolation of the wires 34from each other. Thus, the provision of a coating in each recess whichis thinner than the coating on the interior surface will provide ahigher resistance value in the recesses which results in electricalisolation of the associated wires since the electrons willpreferentially be conducted by the surface coating. The conductivecoating is suitably connected to a resistor 40, which is across thevoltage supply 22 for the purpose of biasing the wires 34 just below thewriting or discharge potential.

In accordance with the above, there has been shown and described hereina novel, useful and simple arrangement for improving the operation of anelectrostatic writing tube, but the particular embodiments or forms ofthe invention described herein are not limitations upon other manners ofpracticing the invention.

I claim:

1. An electrostatic printing tube in which a plurality of conductiveelements are successively scanned by an electron beam for recording on adielectric, the improvement comprising a dielectric face plate in whichsaid elements are carried in parallel relationship and are separated onefrom the other by the dielectric material, said face plate having aplurality of recesses formed in its interior surface with each of saidelements extending from the deepest portion of a respective recess tothe exterior surface of said plate whereby their parallel lengths arereduced to thereby limit their capacitive relationship to each other,and including a conductive surface coating covering the interior surfaceof said plate and extending into said recesses for connecting saidelements in common to a source of bias.

2. The arrangement claimed in claim 1 in which said coating is thinnerin each recess than on other portions of said interior surface wherebysaid thinner coating provides a resistance value for electricalisolation of said elements.

3. An electrostatic printing tube in which a plurality of conductorsextend from the interior to the exterior surface of the dielectric faceof the tube and are charged successively by an electron beam forenabling a discharge through a dielectric recording material forreproducing an image, the improvement comprising an undulating interiorsurface for said face with each of said conductors extending from thepoint at which a respective undulation is closest to the exteriorsurface, and a conductive coating covering said interior surface andthereby connecting said conductors in common, and means connecting saidcoating to a source of bias.

4. An electrostatic printing tube having a plurality of conductiveelements extending from the interior to the exterior of said tube forreproducing respective charges applied thereto by discharge at theexterior end thereof through a dielectric, comprising a dielectric faceplate in which said elements are carried in parallel relationship andare separated one from the other by the dielectric material, said faceplate having a plurality of recesses formed therein with each elementextending from a corresponding recess to the exterior surface of saidplate, and a thin conductive coating on the interior of said plate andin said recesses for connecting each element in common to a bias source.

References Cited in the file of this patent UNITED STATES PATENTS2,291,476 Kernkamp July 28, 1942 2,879,422 Borden et al Mar. 24, 19592,952,796 Crews et a1 Sept. 13, 1960 2,963,606 Crews et al Dec. 6, 19602,978,607 Borden Apr. 4, 1961 FOREIGN PATENTS 574,078 Great Britain Dec.19, 1945

3. AN ELECTROSTATIC PRINTING TUBE IN WHICH A PLURALITY OF CONDUCTORSEXTEND FROM THE INTERIOR TO THE EXTERIOR SURFACE OF THE DIELECTRIC FACEOF THE TUBE AND ARE CHARGED SUCCESSIVELY BY AN ELECTRON BEAM FORENABLING A DISCHARGE THROUGH A DIELECTRIC RECORDING MATERIAL FORREPRODUCING AN IMAGE, THE IMPROVEMENT COMPRISING AN UNDULATING INTERIORSURFACE FOR SAID FACE WITH EACH OF SAID CONDUCTORS EXTENDING FROM THEPOINT AT WHICH A RESPECTIVE UNDULATION IS CLOSET TO THE EXTERIORSURFACE, AND A CONDUCTIVE COATING COVERING SAID INTERIOR SURFACE ANDTHEREBY CONNECTING SAID CONDUCTORS IN COMMON, AND MEANS CONNECTING SAIDCOATING TO A SOURCE OF BIAS.